3 ms·

Just wondering: is rails transactional? What I mean how are race conditions avoided if e. g. two requests are processed at the same time.

gls2ro 6y ago
In case of DB: I think ActiveRecord has #lock (see https://api.rubyonrails.org/classes/ActiveRecord/Locking/Optimistic.html https://api.rubyonrails.org/classes/ActiveRecord/Locking/Opt...) and that together with #transaction (https://api.rubyonrails.org/classes/ActiveRecord/Transactions/ClassMethods.html https://api.rubyonrails.org/classes/ActiveRecord/Transaction...) are enough for my use cases. In case of file uploads to cloud providers: there I don't know for specific method to help with race conditions when transforming the resources.
ryanbrunner 6y ago
Rails has support for database transactions, but depending on what you want to do, things won't be magically transactional all by themselves (that said, it's really just a matter of wrapping transactional code in a block). There are a couple of footguns in Rails involving transactions - by default, validating uniqueness of a column in Rails will be done at the app layer which is prone to race conditions, and with a typical CRUD model for an application, there's nothing in particular preventing overwrites of model data if say, a field was present on a form and two people were editing it, even if the "later" editor made no changes to that particular field. When multiple systems and things other than databases (or multiple databases) are involved, you're generally on your own as well.
- pbowyer 6y ago
  It's important to say that these footguns are not exclusive to Rails. I don't know a single web framework which avoids them - if it exists I'd like to know so I can learn how they do it.
  - RickSullivan 6y ago
    Elixir's Ecto has the best solution to this problem in my experience--it doesn't do database validations on things like uniqueness, but provides easy error handling when constraints are hit. It encourages you to write validations for things that don't need to hit the DB, but actually uses the DB for handling constraints, since it's the real source of truth for data consistency.
- andi999 6y ago
  Thanks. So typical CRUD applications usually run on luck? (or on not beeing unlucky if the average number of request per hour is not so high).
  - msbarnett 6y ago
    Not really? Most CRUD applications go the one extra step of putting a uniqueness constraint on the column instead of just relying on the app layer validation, and comparing hidden time stamps on the form if multiple people might edit the same row simultaneously. It’s exceedingly straightforward. Did you really think thousands of web apps up to and including GitHub and shopify were squeaking by on blind luck? If basic database transactions and integrity weren’t doable in Rails, that’d have had to have been fixed years ago.
    - andi999 6y ago
      Any reference how this is best done with rails?
      - msbarnett 6y ago
        Depends on what you mean by “this”, I suppose. Most of your basic questions are covered by the starter Rails Guide for ActiveRecord, eg) transactions, validations, how to add a uniqueness constraint to the DB in a migration https://guides.rubyonrails.org/active_record_basics.html https://guides.rubyonrails.org/active_record_basics.html The ActiveRecord Queries guide also covers some mechanisms for handling row-level write contention https://guides.rubyonrails.org/active_record_querying.html#locking-records-for-update https://guides.rubyonrails.org/active_record_querying.html#l...
brightball 6y ago
It's got a very helpful transaction block wrapper structure that allows you to do some really interesting things with database transactions. To be perfectly honest, one of the things that I always love about Rails is exactly how good the database layer is with ActiveRecord. I like using the advanced features of my database, especially PostgreSQL, and I've found that it's really easy to do with Rails. The "Scopes" feature of active record that let's you save small snippets of a query and chain them together is fantastic. I've used it to create complex filter functions that combine full text search and coordinate distance as simple methods that can be attached to any query. Being able to add a `.search("fender").distance_from(location, 5, :miles)` onto any query made my life so much easier. It's been a few years, but I wrote about some of my favorites. https://www.brightball.com/articles/rails-gems-to-unlock-advanced-postgresql-features https://www.brightball.com/articles/rails-gems-to-unlock-adv...

gls2ro 6y ago

In case of DB: I think ActiveRecord has #lock (see https://api.rubyonrails.org/classes/ActiveRecord/Locking/Optimistic.html https://api.rubyonrails.org/classes/ActiveRecord/Locking/Opt...) and that together with #transaction (https://api.rubyonrails.org/classes/ActiveRecord/Transactions/ClassMethods.html https://api.rubyonrails.org/classes/ActiveRecord/Transaction...) are enough for my use cases. In case of file uploads to cloud providers: there I don't know for specific method to help with race conditions when transforming the resources.

ryanbrunner 6y ago

Rails has support for database transactions, but depending on what you want to do, things won't be magically transactional all by themselves (that said, it's really just a matter of wrapping transactional code in a block). There are a couple of footguns in Rails involving transactions - by default, validating uniqueness of a column in Rails will be done at the app layer which is prone to race conditions, and with a typical CRUD model for an application, there's nothing in particular preventing overwrites of model data if say, a field was present on a form and two people were editing it, even if the "later" editor made no changes to that particular field. When multiple systems and things other than databases (or multiple databases) are involved, you're generally on your own as well.

pbowyer 6y ago
It's important to say that these footguns are not exclusive to Rails. I don't know a single web framework which avoids them - if it exists I'd like to know so I can learn how they do it.
- RickSullivan 6y ago
  Elixir's Ecto has the best solution to this problem in my experience--it doesn't do database validations on things like uniqueness, but provides easy error handling when constraints are hit. It encourages you to write validations for things that don't need to hit the DB, but actually uses the DB for handling constraints, since it's the real source of truth for data consistency.
andi999 6y ago
Thanks. So typical CRUD applications usually run on luck? (or on not beeing unlucky if the average number of request per hour is not so high).
- msbarnett 6y ago
  Not really? Most CRUD applications go the one extra step of putting a uniqueness constraint on the column instead of just relying on the app layer validation, and comparing hidden time stamps on the form if multiple people might edit the same row simultaneously. It’s exceedingly straightforward. Did you really think thousands of web apps up to and including GitHub and shopify were squeaking by on blind luck? If basic database transactions and integrity weren’t doable in Rails, that’d have had to have been fixed years ago.
  - andi999 6y ago
    Any reference how this is best done with rails?
    - msbarnett 6y ago
      Depends on what you mean by “this”, I suppose. Most of your basic questions are covered by the starter Rails Guide for ActiveRecord, eg) transactions, validations, how to add a uniqueness constraint to the DB in a migration https://guides.rubyonrails.org/active_record_basics.html https://guides.rubyonrails.org/active_record_basics.html The ActiveRecord Queries guide also covers some mechanisms for handling row-level write contention https://guides.rubyonrails.org/active_record_querying.html#locking-records-for-update https://guides.rubyonrails.org/active_record_querying.html#l...

brightball 6y ago

It's got a very helpful transaction block wrapper structure that allows you to do some really interesting things with database transactions. To be perfectly honest, one of the things that I always love about Rails is exactly how good the database layer is with ActiveRecord. I like using the advanced features of my database, especially PostgreSQL, and I've found that it's really easy to do with Rails. The "Scopes" feature of active record that let's you save small snippets of a query and chain them together is fantastic. I've used it to create complex filter functions that combine full text search and coordinate distance as simple methods that can be attached to any query. Being able to add a `.search("fender").distance_from(location, 5, :miles)` onto any query made my life so much easier. It's been a few years, but I wrote about some of my favorites. https://www.brightball.com/articles/rails-gems-to-unlock-advanced-postgresql-features https://www.brightball.com/articles/rails-gems-to-unlock-adv...